Nutating-type actuator



NUTATING TYPE ACTUATOR Filed June 6, 1966 lSheet /v of Hi L? A 4% y /f' 2g if L w Am ,/,f/ 4f j! j jf INVENTORs.

Feb. 18, 1969 J. c. SINGLE-row ET AL 3,428,839

l NUTATING-TYPE AcTUAToR Filed June 6,-1966 sheet 2 of 5 if-ix l, gig

DI iff Feb. 18, 1969 Filed June 6, 19

J. C. SINGLETON ET AL NUTATING-TYPE ACTUATOR JJM raya/IKS'.

Unted States Patent O 12 Claims ABSTRACT OF THE DISCLOSURE A control rod drive of the rack and pinion type is powered by a nutating electric motor having an integrated nutating gear and armature centered on the extended axis of the pinion and contained in a sealed enclosure but powered by electromagnetic means, all of the electrical elements being accessible outside the enclosure.

Brief summary of the inventive field This invention relates to electric motor-transmission assemblies, and particularly to an improved low-speed drive which is compact, simple, rugged and reliable in character, which enables output torque to be applied to a driven member located behind a pressure barrier, as Within a sealed enclosure, with all electrical components nevertheless located outside the enclosure and which does not require the use of running seals.

An object of the invention is to provide an improved drive of the indicated character which develops high torque in proportion to the mass of its moving parts.

Another object of the invention is to provide an improved drive for control rods.

Other objects and advantages will become apparent upon consideration of the present disclosure in its entirety.

Brief description of the figures of drawing FIGURE 1 is a horizontal sectional plan view of a control rod drive incorporating the present invention, taken diametrically through the nutating motor-transmission;

FIGURE 2 is a view which is similar but taken in a vertical plane, showing a modied construction;

FIGURE 3 is a horizontal sectional view of the embodiment of FIGURE 2, on a smaller scale taken substantially on the line III--III of FIGURE 2 and looking in the direction of the arrows, and

FIGURE 4 is a sectional elevational view taken substantially as indicated by the line and arrows IV-IV of FIGURE 3 and looking in the direction of the arrows.

Detailed description of preferred forms of the invention Referring now to the drawing, reference character designates generally the body of a control rod drive assembly within which a rack 12 is vertically slidable, the rack being adapted to be connected to a control rod (not shown) to be actuated. The details of the control rod and its connection to the rack form no part of the present invention and as such devices are well known in the art will require no detailed description. As will be appreciated, the rack is ordinarily directly connected to the control rod, and when the rack and control rod are moved upwardly, the neutron ux and rate of generation of the reactor are increased, while when the rod is lowered, the flux and generation are reduced.

It is desirable to arrange the drive in such manner that in event of a power failure or of any other unusual conditions, the rod can fall back down under gravity into the reactor. Permitting the rods to drop quickly to prevent ICC undesirable buildup is termed scramming It is also desirable that the mass and inertia of moving parts be as small as possible, not only to reduce the time required for the rod to accelerate downwardly during scram, but also to reduce the braking forces required to stop it.

The rack 12 meshes with and is driveable by a pinion 14 fast on a shaft 15 journaled at one end by antifriction bearing 16 in a blind hole in the body. The other end of the shaft is journaled in an antifriction bearing 17 and an integral enlargement of the shaft extends into a shallow annular chamber 20 and is formed as a bevel gear 22 having teeth 24 meshable with the teeth 25 of a nutating gear 26 secured to a nutating armature 28. The armature and nutating gear are rockably but nonrotatably mounted on a ball 30 centered on the common axis of shaft 15 and gear 22, with which the gear 14 and pinion 22 are also coaxial. Gear 22 is held in a perpendicular plane and has a dilerent number of teeth from gear 26 (a difference of a single tooth may be employed) so that a very slow speed rotary drive will be imparted to the gear 22 when gear 26 nutates. Rotation of the armature and nutating gear is prevented by a roller 33 journaled on a radial axis in the periphery of housing 10 and projecting into chamber 20 and into a slot 34 in the periphery of the armature.

It will be noted that no seals are provided on the shaft 15 and water in the rack passage, and in the lateral enlargement 13 thereof which houses the shaft and pinion 14, may therefore enter the chamber 20'. A housing portion 35 forms a closure for the open face of chamber 20 and is sealed to casing portion 10 as by static seals 36, 38, casing portions 10-35 being tightly held together as by studs 40 and nuts 41.

Housing portion 35 has a plurality of spaced circumferentially arranged pole pieces 42, the ends of which are exposed in chamber 20. The pole pieces, formed of magnetic material, are tightly secured and sealed to housing portion 35 by peripheral welds 44, and extend rearwardly into chambers 45 within which are electromagnet windings 46. A sealed and gasketed cover plate 50 is removably secured by screws 48 over the back of casing 35 and closes all of the coil chambers 45. This arrangement permits ready access to the coils so that a quick replacement can be made in event of an electrical breakdown or burnout without violating the integrity of the chamber 20'.

The bearing ball 30 is mounted on an axial pin 52 and the armature is mounted thereon by a socket portion 54 in the armature and a mating socket portion 55 axially formed in a disc 56 forming a part of the armature assembly and secured to the main armature portion 28 by screws 58. Pin 52 is supported in casing portion 35 in a hub plate 60 secured as by screws 62 in a counterbored recess 64 formed in the inner face of casing portion 35. The gear 22 may be provided with a separate hardened center bearing pad 74, as shown.

A plurality of peripherally equally spaced compression springs 64 are trapped in blind holes 65 in the recessed portion of the inner face of casing portion 35 and bear outwardly against abutment collars 66 integrally formed upon pins 68 slidable axially through the holes 65 and through extensions thereof formed in the casing portion 35 and (at 70) in plate 60. The front ends of plungers 68 project into chamber 20 beneath the armature 28 to the extent permitted by their integral collars 66 and the extent of such projection is suicient so that when all of the plungers are fully projected they position the armature and gear 26 in a plane perpendicular to the common axis of the rotating and nutating parts described. When gear 26 is in such transverse position the teeth 24, 25 are out of mesh and spaced from one another throughout their entire peripheral extent, so that gear 22 is declutched and is freely rotatable, freeing the control rod and rack 12 to drop into the reactor.

It will be understood that the electromagnet windings 46 are energized in a peripheral sequence as by a suitable pulse generator (not shown) at a desired rate and in the desired direction to raise or lower the rack and control rod in the normal manner, and it will be understood that a very accurate and slow drive is imparted during such normal actuation, due to the high ratio of the gear reduction. A separate locking device (not shown) but which is also electromagnetic may be provided to hold the rack and rod in any desired or set position. In event of a power failure, such lock is deenergized, and the coils 46 are also deenergized. The armature and nutating gear 26 are thereupon immediately moved to the transverse position by the spring-pressed plungers 68 declutching the drive and permitting scram in the manner indicated.

The inner face of disc 60 is provided with an annular abutment ridge 75 projecting a short distance into chamber in an axial direction beneath the armature 28. The surface facing the armature forms an abutment coacting with the adjacent bottom surface of the armature and limiting the rocking motion of the nutating armature so that the armature does not contact the pole pieces or any other stationary portions other than stop ridge 75. The contacting surfaces of ridge 75 and of the under surface of the armature are so designed as to roll on one another, these surfaces forming circular frustums of the same diameter of identical cones.

The pitch lines of the teeth 24, also lie on conic surfaces, and the pitch cones defined `by the meshing teeth during nutation coincide with the center of nutation of the armature. This permits simple rolling motion and virtually eliminates drag at the teeth.

In the modified construction shown in FIGURES 2-4 many parts are analogous to those of the first embodiment. These are designated by like reference characters distinguished by the addition of the letter a and will require no redescription. The pole pieces 42a project a substantial distance into the chamber 20a and are provided with wedge-shaped ends tapering radially inwardly toward the axis of the assembly to narrow edges which `are inclined outwardly toward their ends and lie on a cone concentric with the axis. The periphery of the armature 28a is provided with conformably wedge-shaped indentations 80 in radial alignment with and proportioned to accurately overfit upon the Wedge-shaped ends of the pole pieces. The wedge-shaped ends of the pole pieces are protected by wear resistant cover plate portions 82 secured thereto and which serve as abutments for the armature, the slotted portions 80 of which strike the plates 82 during nutation. Due to the sloping sides and radial overfitting of the wedge-shaped pole pieces and conformably slotted armature portions 80, the strength of the magnetic field and its effective length are substantially increased.

Compression springs 64a fitted in pockets in the hub plate 60a bear -directly against the underside of the armature 28a to align the latter in a transaxial plane for scram as in the previous embodiment.

A gimbal-type support for the armature permits the armature to rock universally during nutation without permitting axial rotation thereof. The hub plate portion 60a is keyed against rotation in body portion a as by pin 83 and supports the gimbal bearing on a pin 52a keyed in the hub. Inner and outer gimbal rings, 84, 85 are provided, the latter ring carrying the bevel gear 25a which is secured to and nutates with the armature 28a and meshes with gear 22a as in the first embodiment. The inner gimbal ring 84 is carried on a support 86 secured to the hub 60a and locked against rotation with respect thereto and with respect to the pin 52a by a cross pin 87.

This detailed description of preferred forms of the invention, and the accompanying drawings, have been furnished in compliance with the statutory requirement to set forth the best mode contemplated by the inventors of carrying out the invention.

What is claimed is:

1. A control rod drive comprising a traveling rack, a sealed casing within which the rack is longitudinally movable, a gear rotatable in the casing on a fixed axis and meshing with the rack to drive the latter, a second gear rotatable on a fixed axis in the casing and drivingly connected to the first mentioned gear, a nutating gear meshing with the second gear, and electromagnetic means for imparting nutational motion to the nutating gear, including magnetic pole portions exposed within but sealed with respect to said casing, and electrically powered energizing means for the pole portions accessible from outside the casing without distrubing the sealed condition of the casing or pole portions.

2. A drive as defined in claim 1 wherein the first and second mentioned gears are rigidly mounted on a common shaft, the nutating gear 4being concentric with the axis of said shaft and held against rotation about such axis and engageable with the second gear only when tilted, and spring means yieldably urging said nutating gear to a c0- axial, non-tilted, non-meshing position.

3. A control rod drive as defined in claim 1 including armature means within the casing coacting with said pole portions and affixed to the nutating gear for nutation therewith, including a plurality of pole portions of low retentivity appurtenant to means for inducing a varying magnetic flux in said pole portions in a timed peripheral sequence to cause nutating motion by progressively attracting peripherally spaced portions of the armature means, means supporting the armature means for universal rocking motion, and stop means limiting such rocking motion and preventing unwanted physical contact between the armature means and pole portions.

4. A drive as defined in claim 3 in which said means supporting the armature means includes bearing portions concentric with said fixed axis, said stop means being radially outspaced from said bearing portions.

5. In a drive as defined in claim 1, an annular armature portion fast to the nutating gear, means holding said armature portion and nutating gear against axial rotation, magnetizable means including pole portions for progressively tilting the gear about different transverse axes to impart nutation thereto by causing movement of peripheral portions of the armature portion toward and from the pole portions, said armature and pole portions having interfitting parts which overlap in directions lengthwise of said fixed axis.

6. A drive as defined in claim 1 in which said casing forms a part of a common sealed enclosure which also encloses the means for imparting nutational motion, said last named means comprising a nutating electro-magnetically powered motor including an armature portion within said sealed enclosure and electromagnet means outside the sealed enclosure.

7. A nutating motor-transmission assembly including an armature, means causing nutation of the armature about a rocking center, a nutating bevel gear carried by the armature and having the apex of its pitch cone substantially at said rocking center, and a driven bevel gear meshing with the nutating gear.

8. A drive as defined in claim 1 wherein the projected pitch lines of the meshing teeth of the second gear and of the nutating gear extend substantially through the center of nutation.

9. A drive as defined in claim 3 wherein said stop means comprises an annular nutating bearing surface portion fast with respect to the armature and nutating gear and a fixed bearing surface portion of the same circumferential length as the nutating bearing surface, said bearing surface portions being in rolling contact along a path concentric with respect to the axis of nutation.

10. A drive as defined in claim 1 wherein the nutational motion occurs by rocking about a fixed center lying subsecond mentioned gears are coaxial and the center of 6 nutation lies on the same axis.

References Cited UNITED STATES PATENTS Pagie 74-800 Plensler 310-82 Roman 310-80 Bouvier 310-82 9/1960 Sundt 74-800 11/1961 Baumgarten 176-36 5/1966 Anderson 310-82 3/ 1967 Dickson 176-36 9/1967 Gifford 310-80 FOREIGN PATENTS 8/ 1928 Netherlands.

10 I D MILLER, Primary Examiner.

U.S. C1. X.R.

UNTTED STATES PATENT oEEICE CERTIFICATE OF CORRECTION Patent No. 3,428,839 February I8, 1969 John C. Singleton et al.

in the above identified It is certified that err-or appears rected as patent and that Said Letters Patent are hereby co1` Shown below:

Column 4, lines 27 "slow should read low of low retentivity Column 2, line 20,

lurality of pole portions and 28, cancel "including a p appartenant" Signed and sealed this 31st day of March 1970.

(SEAL) Attest:

WILLIAM E. SCHUYLER, J

Edward M. Fletcher, Jr. Attesting Officer Commissioner of Patents 

